The invention relates to heat treatable coated glass panes with a low-e and/or solar control coating. The invention also relates to methods of manufacturing said panes.
Heat treated glass panes which are toughened to impart safety properties and/or are bent are required for a large number of areas of application, for example for architectural or motor vehicle glazings. It is known that for thermally toughening and/or bending glass panes it is necessary to process the glass panes by a heat treatment at temperatures near or above the softening point of the glass used and then either to toughen them by rapid cooling or to bend them with the aid of bending means. The relevant temperature range for standard float glass of the soda lime silica type is typically about 580-690° C., the glass panes being kept in this temperature range for several minutes before initiating the actual toughening and/or bending process.
“Heat treatment”, “heat treated” and “heat treatable” in the following description and in the claims refer to thermal bending and/or toughening processes such as mentioned before and to other thermal processes during which a coated glass pane reaches temperatures in the range of about 580-690° C. for a period of several minutes, e.g., for up to about 10 minutes. A coated glass pane is deemed to be heat treatable if it survives a heat treatment without significant damage, typical damages caused by heat treatments being high haze values, pinholes or spots.
The inventors of the present invention found that the parameter “haze” usually referred to when characterising the heat treatability of low-e and/or solar control coatings is often insufficient, as it does not fully reflect all types of defects that may arise during coating, heat treating, processing and/or handling of coated glass panes. They found that several low-e and/or solar control coated panes described as heat treatable did not withstand all of the tests simulating ordinary environmental influences during storage, transport and use of the coated glass panes before and after a heat treatment, and the mechanical and chemical conditions acting on the coated glass panes during usual handling and processing steps, without significant visible damage.
The invention more particularly concerns coated glass panes wherein the coating comprises at least a lower anti-reflection layer, a silver-based functional layer, a barrier layer, and an upper anti-reflection layer. In such coatings the barrier layer serves to protect the silver-based functional layer against detrimental influences during production and subsequent heat treatments. The anti-reflection layers serve to anti-reflect the functional layer to achieve a high light transmittance and low reflectance. The barrier layer may contribute to the anti-reflecting effect of the subsequent anti-reflection layer.
DE10042194 describes an IR reflecting layer system with layers of gradually changing composition. At least one IR reflecting metal layer such as Ag, Au or Cu is present, with a Nb2O5 based lower dielectric layer. No specific examples are disclosed, although potential stacks with a TiO2 barrier layer and ZnO/TiO2 topcoats are mentioned. There is no discussion of mechanical durability properties or heat treatability of the stacks in DE10042194.
EP1140721 describes silver based heat-treatable low-e coatings that avoid the use of protective metal primer (barrier) layers such as NiCrOx or TiOx over silver layers. The stacks contain at least two silver-based layers and utilise single aluminium doped zinc oxide barrier layers.
EP0304234 describes a coated pane with a silver-based layer that is protected from staining by providing a barrier layer comprising the oxides of at least two metals. TiO2/ZnO/TiO2 layer arrangements above the silver layer are mentioned. The barrier layers are said to be non-transmissive of moisture and other staining agents, amorphous and free of grain boundaries.
EP0593883 describes coated panes with high light transmittance and IR reflection properties. The coating includes a metallic double layer of for instance a titanium barrier layer deposited on top of a silver layer. A triple dielectric layer of for example ZnO/TiO2/ZnO is deposited on top of the barrier layer.
U.S. Pat. No. 5,302,449 describes high light transmittance, low-e coated panes that exhibit a neutral colour through a wide range of angles of incidence of light. The coating uses a dual silver layer arrangement and sacrificial barrier layers of metal oxides such as TiO2. The outermost barrier layer may be coated with one or more additional oxide layers.
It is well known to use substoichiometric NiCrOx as a sacrificial barrier layer (e.g. see US2009/0197077 and WO 2010/073042) since it affords favourable heat treatability and subsequent mechanical durability (see DE102008007981 and US20100178492). However, the presence of a NiCrOx layer complicates manufacturing because of the critical conditions required to deposit a layer of the correct stoichiometry. The use of NiCrOx furthermore leads to significant changes of optical properties, i.e. light transmittance, colour, absorption, light reflectance of the coating stack during a heat treatment. Therefore it would be attractive to provide a coated glass pane that exhibits good heat treatability and mechanical durability without the need for a substoichiometric NiCrOx sacrificial barrier layer above a silver-based functional layer.